The alkali-zinc battery has a high energy density and a high power characteristic. Because of a high solubility of zinc, however, zinc acid ions existing in electrolyte at the time of charging have deposited on an anode in dendrite form or spongy form, a short-circuiting piercing through the separator has taken place, or a shape change has occurred to minimize utilization factor; so that a cycle life of a battery has been short.
A micro-porous membrane comprising polypropylene, polyethylene etc. subjected only to surface active agent treatment has been used for a conventional separator for alkali-zinc battery. Such a separator has a desirable property for use in a sealed-type battery in which O.sub.2 gas is absorbed by a zinc electrode, because O.sub.2 gas is permeable through it. However, since it is subjected only to the surface active agent treatment, its hydrophilic property is weakened while it is immersed in electrolyte. Further, a mechanism wherein ZnO is gradually precipitated in micro-pores to bring about short-circuiting, i.e. a dendrite short-circuiting, can not be avoided sufficiently so that it is not suitable for an application requiring a long-term storage or a charge/discharge cycle life of a long period.
In order to improve the above disadvantages, there has been used a separator fabricated by a semi-permeable membrane and a micro-porous membrane placed one upon another. However, the permeability of O.sub.2 gas can not be expected in these membranes.